The DC14 is much better than an 04 for the following reasons;
-Better wand setup (more comfortable and the handle isn't at the end of the wand like a DC04)
-Larger pre filter captures more allergens and should have longer lasting suction vs the smaller Dc04 filter
-Dc04 cyclones are not as efficient as DC14 ones, I can guarantee you that after fitting brand new filters to a DC04 and using it for a week, there will be some dust on the filter. A DC14's pre filter stays cleaner for longer
-Dc14's are much more powerful and robust. How many cracked parts do you see on an old DC04 vs an old DC14? DC14's can take a good pounding. If there's anything to go wrong with them it's either a ripped hose, cracked chassis, cracked cleaner head which is unlikely.
A DC04 is prone to wands snapping if knocked over, wand caps being annoying if using the wand without tools, thinner ducting so more likely to get clogged and less airflow. Dc04 plastic is also more fragile than on DC14's due to being earlier models and the cyclone handles can also break especially on early British models. If it's a 2004/05 Dc04 then durability shouldn't be an issue.
A DC14 is a better machine overall in every single way. I can't fault a DC14. The only thing I dislike is the crevice tool which has a bend in i but then again it can be useful for awkward gaps in a car or something. It has a large hole as well which is good for airflow. Crevice tools concenttrate the suction so this is good. You can always tape it up as well if you like.
DC14's are easier to service and quicker as well believe it or not. 6 screws and your already into the motor on a non cluched (3 extra on a clutched) and a DC04 has 8 screws for the motor housing alone! Plus 2 for the diffuser
Well I'm going over the top so I will hush for now :)